The invention relates to a fuel injection mechanism for mixture compressing, externally ignited internal combustion engines, particularly one provided with an injection location in the air induction line, within which are consecutively disposed an airflow measuring element and an arbitrarily manipulatable throttle valve. The airflow measuring element is moved in accordance with the airflow rate and against a restoring force, thereby displacing the movable component of a fuel valve for the apportionment of a fuel quantity proportional to the air quantity, the fuel valve being located within the rotating shaft of the air measuring element.
The pressure difference across the fuel valve is held constant by a differential pressure valve constructed as a flat seat valve having a membrane as movable valve member. One surface of the membrane experiences fuel pressure from upstream of the metering valve while the other surface is exposed to fuel pressure prevailing downstream of the metering valve and additionally the force of a spring.
Fuel injection mechanisms of this kind have the purpose of automatically producing a favorable fuel-air mixture for all of the operational conditions of the internal combustion engine, in order to effect the complete combustion of the fuel, and thereby to avoid or at least reduce greatly the formation of noxious exhaust gas constituents, in conjunction with the highest possible outpt of the internal combustion engine, or the least possible fuel consumption. The fuel quantity must therefore be very precisely apportioned in correspondence to the requirements of each given operational condition of the internal combustion engine.
In known fuel injection systems of this type, an enriched fuel-air mixture is obtained during the warm-up phase of the engine by providing a bimetallic spring which engages the differential pressure valves and causes an increase of the differential pressure during warm-up. Inasmuch as shortly after the engine has started, the cylinder walls become warm and any fuel condensation no longer takes place, it is suitable for the purpose of fuel economy and for a reduction of the toxic exhaust gas components to reduce the fuel enrichment somewhat so as to obtain smooth and optimum operation of the engine.